Road vehicles of which the rear wheels can be steered as well as the front wheels in many instances employ quite complicated control arrangements for the rear wheel steering gear. Such arrangements can be responsive to a variety of factors, in addition to the steering angle applied by the driver to the front wheel steering gear, for example, the vehicle body movement as sensed by one or more inertial sensors, and electrical inputs derived from such factors are treated in a computer which provides an electric command signal which is converted, for example, electro-hydraulically, into a wheel steering movement. These arrangements are necessarily subject to the possibility of failure, which would make the vehicle difficult to control and could thus result in a accident.
It is thus an object of the invention to provide a powered vehicle steering system with biassing means for returning the system to a neutral and straight ahead position in the event of system failure.
It is a further object of the invention to provide an electro-hydraulic steering system with mechanical fail safe means operative in the event of electrical and/or hydraulic failure.
It is also an object of the invention to provide means for minimising or eliminating the adverse effects of rear wheel steering system failure in a vehicle with front and rear wheel steering.